In integrated circuit fabrication, metal lines are often in contact with dielectric layers. For example, a trench in a dielectric layer may be formed and then metal deposited in the trench to form a metal line. It may be desirable to use copper, with its low resistivity, to form these metal lines. Copper, however, due to its diffusivity in a dielectric layer, should not be in direct contact with dielectric layers. Therefore, a barrier layer may be deposited on the dielectric layer before depositing copper to separate the copper from the dielectric layer. A commonly used metal barrier layer is tantalum nitride (TaN). Tantalum (Ta) is commonly deposited on a metal barrier layer of tantalum nitride to improve the adhesion of copper. To maximize the amount of copper in the trench so that the electrical line resistance may be reduced, the TaN and Ta layers may be thin and conformal. In some instances, tantalum may be used alone as a metal barrier layer.